# std::ranges::equal_to

From cppreference.com
< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
struct equal_to; |  | (since C++20)

Function object for performing comparisons. The parameter types of the function call operator (but not the return type) are deduced from the arguments.

### Nested types

Nested type | Definition
`is_transparent` | unspecified

### Member functions

operator() | checks if the arguments are equal (public member function)

## std::ranges::equal_to::operator()

template< class T, class U > constexpr bool operator()( T&& t, U&& u ) const; |  |

Given the expression std::forward<T>(t) == std::forward<U>(u) as expr:

- If expr results in a call to built-in operator== comparing pointers, given the composite pointer type of t and u as `P`:

  - For the two converted pointers (of type `P`), if one pointer precedes the other in the implementation-defined strict total order over pointers, returns false, otherwise returns true.
  - If the conversion sequence from `T` to `P` or the conversion sequence from `U` to `P` is not equality-preserving, the behavior is undefined.

- Otherwise:

  - Returns the result of expr.
  - If std::equality_comparable_with<T, U> is not modeled, the behavior is undefined.

This overload participates in overload resolution only if std::equality_comparable_with<T, U> is satisfied.

### Notes

Compared to std::equal_to, `std::ranges::equal_to` additionally requires `!=` to be valid, and that both argument types are required to be (homogeneously) comparable with themselves (via the `equality_comparable_with` constraint).

### Example

| This section is incomplete Reason: no example

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 3530 | C++20 | syntactic checks were relaxed while comparing pointers | only semantic requirements are relaxed

### See also

equal_to | function object implementing x == y (class template)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/utility/functional/ranges/equal_to&oldid=167647"